SYSTEMS AND METHODS FOR DETECTING OUT-OF-PLANE LINEAR ACCELERATION WITH A CLOSED LOOP LINEAR DRIVE ACCELEROMETER

• US 20100024552A1
• Filed: 07/31/2008
• Published: 02/04/2010
• Est. Priority Date: 07/31/2008
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Honeywell International Inc.
• Inventors: Foster, Michael J.
• Granted Patent: US 8,171,793 B2
• Time in Patent Office: Days
• US Class Current: 73/514.290
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/131 with electrostatic counterbalancing means
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration
• CPC Class Codes: G01P 2015/0834 the mass constituting a pendulum having the pivot axis disposed symmetrically between the longitudinal ends, the center of mass being shifted away from the plane of the pendulum which includes the pivot axis
• CPC Class Codes: G01P 2015/0882 for providing damping of vibrations

Abstract

Systems and methods sense out-of-plane linear accelerations. In an exemplary embodiment, the out-of plane linear accelerometer is accelerated in an out-of-plane direction, wherein the acceleration generates a rotational torque to an unbalanced proof mass. A rebalancing force is applied to at least one plurality of interleaved rotor comb tines and stator comb tines, wherein the rebalancing force opposes the rotational torque, wherein the rotor comb tines are disposed at an end of the unbalanced proof mass, and wherein the stator comb tines are disposed on a stator adjacent to the end of the unbalanced proof mass. An amount of acceleration is then determined based upon the applied rebalancing force.

Claims

1. A method that determines an out-of-plane acceleration of an accelerometer, the method comprising:

accelerating the accelerometer in an out-of-plane direction, wherein the acceleration generates a rotational torque to an unbalanced proof mass;

applying a rebalancing force to at least one plurality of interleaved rotor comb tines and stator comb tines, wherein the rebalancing force opposes the rotational torque, wherein the rotor comb tines are disposed at an end of the unbalanced proof mass, and wherein the stator comb tines are disposed on a stator adjacent to the end of the unbalanced proof mass; and

determining an amount of acceleration based upon the applied rebalancing force.

2. The method of claim 1, wherein the stator comb tines are offset from the rotor comb tines.

3. The method of claim 1, wherein applying the rebalancing force comprises:

applying a voltage to the stator.

4. The method of claim 3, further comprising:

determining the amount of acceleration based upon the applied voltage.

5. The method of claim 1, wherein the unbalanced proof mass includes a first portion defined by a first mass, wherein the unbalanced proof mass further includes a second portion defined by a second mass different from the first mass, and wherein an axis of rotation is between the first portion and the second portion.

6. The method of claim 1, wherein the rebalancing force is a first rebalancing force applied to a plurality of interleaved first stator comb tines and first rotor comb tines disposed at a first end of the unbalanced proof mass, and further comprising:

applying a second rebalancing force to at least one plurality of interleaved second rotor comb tines and second stator comb tines, wherein the second rebalancing force opposes the rotational torque, wherein the second rotor comb tines are disposed at a second opposing end of the unbalanced proof mass, and wherein the second stator comb tines are disposed on a second stator adjacent to the second end of the unbalanced proof mass; and

determining an amount of acceleration based upon the applied first and second rebalancing forces.

7. A closed loop linear drive accelerometer, comprising:

an unbalanced proof mass with a first proof mass portion defined by a first mass and a second proof mass portion defined by a second mass, the second mass being different from the first mass;

a plurality of first proof mass comb tines at a first end of the unbalanced proof mass;

a plurality of first stator comb tines interleaved with the plurality of first proof mass comb tines, the plurality of first stator comb tines offset from the plurality of first proof mass comb tines;

a plurality of second proof mass comb tines at a second end of the unbalanced proof mass;

a plurality of second stator comb tines interleaved with the plurality of second proof mass comb tines, the plurality of second stator comb tines offset from the plurality of second proof mass comb tines; and

a controller operable to apply a rebalancing force to at least one of the plurality of interleaved first proof mass comb tines and first stator comb tines and the plurality of interleaved second proof mass comb tines and second stator comb tines, wherein the rebalancing force opposes a rotational torque of the unbalanced proof mass generated in response to an out-of-plane acceleration of the unbalanced proof mass, wherein the controller is operable to determine an amount of acceleration based upon the applied rebalancing force.

8. The closed loop linear drive accelerometer of claim 7, further comprising:

at least one flexure configured to couple the unbalanced proof mass to an anchor, and configured to define an axis of rotation between the first proof mass portion and

the second proof mass portion, wherein the rotational torque is about the axis of rotation.

9. The closed loop linear drive accelerometer of claim 7, wherein a first gap defines a first capacitance between the plurality of first proof mass comb tines and the plurality of first stator comb tines, wherein a second gap defines a second capacitance between the plurality of second proof mass comb tines and the plurality of second stator comb tines, and wherein a linear out-of-plane acceleration of the unbalanced proof mass generates the rotational torque changes the first capacitance and the second capacitance.

10. The closed loop linear drive accelerometer of claim 7, wherein the controller comprises:

a closed loop linear drive accelerometer controller electrically coupled to the plurality of first stator comb tines and the plurality of second stator comb tines, and configured to apply a rebalancing voltage to at least one of the plurality of first stator comb tines and the plurality of second stator comb tines that substantially counteracts a rotational torque of the unbalanced proof mass.

11. The closed loop linear drive accelerometer of claim 7, further comprising:

a ground plate disposed below at least the plurality of first proof mass comb tines and the plurality of first stator comb tines.

12. The closed loop linear drive accelerometer of claim 7, wherein a first tine mass of the first proof mass comb tines is greater than a second tine mass of the first stator comb tines, and wherein a third tine mass of the second proof mass comb tines is less than a fourth tine mass of the second stator comb tines, such that the first mass of the first proof mass portion is greater than the second mass of the second proof mass portion.

13. The closed loop linear drive accelerometer of claim 7, further comprising:

a gas dampening compensation volume disposed in the first proof mass portion such that the first mass of the first proof mass portion is less than the second mass of the second proof mass portion; and

a gas dampening compensation volume disposed on a side of the second proof mass adjacent to a substrate, wherein an area of the gas dampening compensation volume is substantially equal to an area of the mass reduction aperture,

wherein a gas dampening of the first proof mass portion is substantially equal to a gas dampening of the second proof mass portion.

14. A Micro-Electro-Mechanical Systems (MEMS) device comprising:

an unbalanced proof mass with a first proof mass portion defined by a first mass and a second proof mass portion defined by a second mass, the second mass being different from the first mass;

a gas dampening compensation volume disposed in the first proof mass portion such that the first mass of the first proof mass portion is less than the second mass of the second proof mass portion; and

a gas dampening compensation volume disposed on a side of the second proof mass portion adjacent to a substrate, wherein an area of the gas dampening compensation volume is substantially equal to an area of the mass reduction aperture,

wherein a gas dampening of the first proof mass portion is substantially equal to a gas dampening of the second proof mass portion.

15. The MEMS device of claim 14, further comprising:

a plurality of first proof mass comb tines at a first end of the unbalanced proof mass;

a plurality of first stator comb tines interleaved with the plurality of first proof mass comb tines, the plurality of first stator comb tines offset from the first plurality of proof mass comb tines;

a plurality of second proof mass comb tines at a second end of the unbalanced proof mass; and

a plurality of second stator comb tines interleaved with the plurality of second proof mass comb tines, the plurality of second stator comb tines offset from the plurality of second proof mass comb tines.